Process of treating gas



Jan. 30, 1934. M. SHOELD PROCESS OF TREATING GAS Filed May 5, 1931 INVENTOR. 070/795/906/0. BY aw 02 W ATTOR Y.

STATES PATENT OFFICE PROCESS OF TREATING GAS Mark Shoeld, Mount Lebanon Township, Allegheny County, Pa., assignor to The Koppers Company of Delaware, a corporation of Delaware Application May 5, 1931. Serial No. 535,157

3 Claims. (01. 23-450) This invention relates to processes of treating It is forced to the top of the compartment 1 and gas and more particularly to the manufacture of sprayed into the sa e y means of the Sprays relatively pure carbon dioxide from gas mixtures The solution passes downwardly through the containing the same. compartment in the form of finely divided drops, The present invention comprises an improved and gas containing carbon dioxide fed through 0 process by which gas containing carbon dioxide the inlet 6 passes upw y through the compartis brought into intimate contact with a solution ment 1 in countercurrent relationship with the containing alkali carbonate whereby alkali bisolution. Very eflicient absorption of carbon dicarbonate solution is formed and the resulting sooxide is brought about by this intimate contact lution is then treated with steam to decompose 0f the g With the Solutieh- The Carbon dioxide 65 the bicarbonate. The carbonate solution which is i P act a y Completely removed therefrom and re-formed is reused for the absorption of addithe residual gases pass O Of the Compartment tional carbon dioxide. 1 t r u h th utl t '7- Examples of apparatus hi h may he used in The carbon dioxide reacts with the carbonate the pregent process are Shown in the accompany to form bicarbonate and the resulting solution ing drawing i passes from the compartment 1 through the plpe Figure 1 is a sectional view, partly in eleva- 10 to the Sprays and d9wnwardly through the tion, of one f r of apparatus; and bed of steel turnings 5 1n the compartment 2. Figure 2 is an elevational view, partly in sec- Steam from the 13 15 passed upwardly tion, of another form of apparatus through the steel turnings countercurrent to the 75 Referring to Fig 1 the apparatus shown bicarbonate solution. The bicarbonate 1s oecom hereby and there is a liberation of subprises a tower divided into two compartments 1 posed. t

tantially pure carbon dioxide which passes out and 2 by a partition 3. These compartments are partially filled with any desired form of material of the compartment 2 through the plpe In the process of the present invention I prefer to bring about the desired contact between gas and liquid. I compartment 1 for instance to use solut1ons of potassium carbonate or potash rather than sodium carbonate or soda ash since Wooden hurdles 4 may be employed m it has been found that for high-temperature panmem' 2 E tummgs 5 m used other absorption, potassium carbonate is the more eflicontact matenals such as spiral tile or coke are Giant The process is Started t ti setlsfactorycontaining substantially to potassium lnlet 6 for gas Contammg carbon dloxlde carbonate and its circulation is so regulated that is situated near the bottom of the compartment when it reaches t lower portion of compart- 1 im d a y b l the f An Outlet ment 1 it has cooled to substantially to C. '7 f ee e Whleh Carbon rdlOXlde has been At this temperature range it has been found that moved 1s situated near the top of the compartmg' m t of Carbon di id absorption by merit potash solution is at its optimum.

p ays 8 ar p s t d in p tm 1 above While the apparatus is in operation, the soluthe hurdles a ep 9 are posltloned abQVe tion entering compartment 1 contains primarily the st tu 5 1n the Gem-Pertinent A P1116 alkali carbonate but also some bicarbonate since 10 formi a Seal 11 leads from the bottom of the bicarbonate is not usually completely decome p t 1 t0 the p y A P p 12 leads posed in the compartment 2. The steam which is from the bottom f Co p 2 t0 the Sprays used in the compartment 2 may be exhaust steam 3 Provided in the p of Compartment from engine driven compressors employed for 45 A p 3 ha a valve 1418 connected to the compressing the carbon dioxide gas removed compartment 2 and conducts steam into this comthrough th pipe 17 from the compartment 2, In partme t be at ape o a plate 16 which its travel upwardly through the compartment 2, ports the Steel turnings Ah Outlet P p the steam is practically all condensed and subas is provided near the top of th mp r m stantially all of this condensed steam is re- 5 2 above the steel turnings 5. evaporated when the solution is passed down- In the operation of th s m f apparatus, alwardly through the compartment 1. In this kali carbonate solution is passed into the system manner a proper solution concentration is mainthrough a pipe 18 having a valve 19 and connected tained. to the pipe 12. By means of a pump 20 the de- It is desirable to provide an auxiliary heater 55 sired amount of solution is kept in circulation. in the form of a closed steam coil 21 in the bottom of the compartment 2. The supply of steam to the coil is controlled by a valve 22 which under normal conditions is kept closed. By means of this auxiliary heater, greater flexibility in the system is obtained.

The carbon dioxide passing out through the pipe 17 is substantially 100% pure and is at a temperature slightly above the temperature of the entering solution and contains only water vapor corresponding to the water vapor pressure of the solution at this point. Water vapor is easily removed by cooling the gas to room temperature or lower.

The gases which are treated are obtained by burning coke or from lime kilns or blast furnace stoves. Blast furnace stove gas contains as high as 27% or 28% carbon dioxide and ordinarily 20% to 25%. These gases may be previously cooled to about atmospheric temperatures and pretreated to remove dust and other materials such as sulphur dioxide and hydrogen sulphide.

Instead of building the compartments 1 and 2 as one unit as indicated in Fig. 1, they may be built as separate units as shown in Fig. 2, in which the tower 24 and the tower 25 correspond respectively to compartments 1 and 2. The gas containing carbon dioxide enters the tower 24 through a pipe 26 and the treated gas passes out through a pipe 27.

The bicarbonate solution is pumped from the bottom of the tower 24 by means of a pump 28 through a pipe 29 to the top of the tower 25 and sprayed by means of sprays 30. The steam for converting the bicarbonate solution passes into the bottom or" the tower 25 through a pipe 31. A closed steam coil 32 may be provided to serve as an auxiliary heater. The carbon dioxide formed leaves the tower 25 through a pipe 33.

The solution at the bottom of the tower 25 is pumped by means of a pump 34 through a pipe 35 to the top of the tower 24 and sprayed therein by means of sprays 36. Both towers contain the desired contact material.

In the apparatus shown in both figures, the size of the chamber, which may be termed the actifier, in which the bicarbonate is decomposed to form carbon dioxide may be less than half the size up to substantially the same size as the chamber in which the absorption takes place. The actifier may be advantageously made smaller due to the fact that the reaction velocity in the actifier is apparently more than double that in the absorber. The reason for this is that there is an absence of large quantities of permanent gases in the actifier which in turn considerably affects the film coeflicient of the carbon dioxide transfer.

In all cases the actifier and the absorber should be properly insulated.

In the absorber the requisite cooling of the solution coming from the actifier takes place by the evaporation of water and this evaporation of water is counterbalanced by the condensation of steam in the actifier. The concentration of the solution passing from the actifier to the absorber is substantially uniform at all times. In previous processes, tanks of bicarbonate solution were boiled to obtain carbon dioxide whereby the sodium carbonate solution formed becomes unduly concentrated and it becomes necessary to constantly replace the water lost in the boiling process.

The solution entering the actifier at substantially 70 to C. tends to cool the gases passing up through the actifier chamber, and particularly in the upper regions thereof. In this way most of the steam is condensed so that substantially pure carbon dioxide passes out.

One advantage of the present invention is that relatively large and expensive apparatus, including the heat exchangers used in the ordinary process, are eliminated. The simplicity of the present apparatus with its attendant low first cost is also an important advantage. Another distinct advantage is that by the countercurrent action obtained in the actifier it is possible to decompose the bicarbonate to a considerably greater extent than when a boiler is used for this purpose.

I claim as my invention:

1. A process of preparing substantially pure carbon dioxide from gases containing the same, which process comprises spraying a hot solution containing alkali carbonate and bicarbonate into a chamber in contact with a relatively cooler gas containing carbon dioxide whereby the solution is cooled and carbon dioxide is absorbed, converting alkali carbonate to alkali bicarbonate, conducting the cooled solution to an extractor chamber at substantially that temperature at which it discharges from the carbon dioxide absorption chamber, spraying the resulting cooled solution at substantially said temperature in the extractor chamber in direct contact with steam, condensing steam in the said latter solution while heating the said latter solution with the said steam to decompose bicarbonate therein and to form carbon dioxide, and returning the so heated solution to the carbon dioxide absorption chamber at substantially that temperature at which it discharges from the extractor chamber and spraying it as aforesaid in the carbon dioxide chamber, whereby condensate from the extractor chamber is evaporated off by the contact with the carbon dioxide gas and the solution cooled thereby.

2. In a process of preparing substantially pure carbon dioxide from gases containing the same, in which process alkali bicarbonate solution is heated in an actifier zone to form carbon dioxide and the resulting alkali carbonate-containing solution is passed into an absorption zoneto absorb carbon dioxide from gases, passing solution containing alkali bicarbonate from the said absorption zone into the said actifier zone in the form of a spray and into direct contact with steam to decompose the bicarbonate and to form carbon dioxide and alkali carbonate, removing carbon dioxide from the said actifier zone in substantially pure form, passing the carbonate solution directly from the said actifier zone into the said absorption zone without intermediate heating or cooling of the said carbonate solution, contacting a spray of the carbonate solution in the said absorption zone with gas containing carbon dioxide to absorb carbon dioxide from the-said gas and to form alkali bicarbonate, and passing the resulting bicarbonate from the said absorption zone to the said actifier zone to obtain additional carbon dioxide, the contact of the solution with steam in the said actifier and the contact of the solution with gas in the said absorption zone being conducted to effect such heating of'the solution in the said actifier zone and such cooling of the solution by the passage of vapors out with the waste gases from said absorption zone that the process carries on continuously without accumulation of excess water or excessive rise in temperature.

3. In a process of preparing substantially pure carbon dioxide from gases containing the same,

in which process alkali bicarbonate solution is heated in an actifier zone to form carbon dioxide and the resulting alkali carbonate-containing solution is passed into an absorption zone to absorb carbon dioxide from gases, passing solution containing alkali bicarbonate from the said actifier zone in the form of a spray and into direct contact with steam to decompose the bicarbonate and to form carbon dioxide and alkali carbonate, removing carbon dioxide from the said actifier zone in substantially pure form, passing the carbonate solution directly from the said actifier zone into the said absorption zone without intermediate cooling of the said carbonate solution, contacting a spray of the carbonate solution in the said absorption zone with gas containing carbon dioxide to absorb carbon dioxide from the said gas and to form alkali bicarbonate, and passing the resulting bicarbonate from the said absorption zone to the said actifier zone to obtain additional carbon dioxide, the contact of the solution with steam in the said actifier zone and the contact of the solution with gas in the said absorption zone being conducted to effect condensation of steam in the said actifier zone substantially equal in amount to the vapors passing out with the Waste gases :from the said absorption zone.

MARK SHOELD. 

